Conduit and method of forming

ABSTRACT

A thin ribbon spirally wound polymer conduit and method of forming, wherein a helical reinforcing bead is interposed adjacent overlapping layers of ribbon. Further, a method of continuously forming spirally wound conduit wherein a sacrificial layer, preferably having a different base polymer to that of the conduit, is first applied to the former before the conduit is formed overtop.

This patent application is a continuation of U.S. patent applicationSer. No. 14/614,209, filed Feb. 4, 2015 and entitled “CONDUIT AND METHODOF FORMING,” which is a continuation of U.S. patent application Ser. No.11/862,875, filed Sep. 27, 2007 and entitled “CONDUIT AND METHOD OFFORMING,” which is a continuation of U.S. patent application Ser. No.10/656,574, filed Sep. 5, 2003, now U.S. Pat. No. 7,291,240, issued Nov.6, 2007 and entitled “METHOD OF FORMING A CONDUIT USING A WOUNDSACRIFICIAL LAYER,” which claims priority from New Zealand PatentApplication No. 521274, filed Sep. 9, 2002 and New Zealand PatentApplication No. 521364, filed Sep. 11, 2002, all of which disclosuresare hereby incorporated by reference. In addition, any and allapplications for which a foreign or domestic priority claim isidentified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference in their entirety.

BACKGROUND TO THE INVENTION 1. Field of the Invention

The present invention relates to components for breathing circuits andin particular to conduits for use in the limbs of breathing circuits.The invention also relates to methods of manufacturing such conduits.

2. Summary of the Prior Art

In assisted breathing, particularly in medical applications, gases aresupplied and returned through conduits. Such conduits are ideally lightand flexible to achieve the highest possible level of comfort for thepatient. In the prior art, thin walled conduits are known which includehelical or annular reinforcing ribs which act to give the conduit betterresistance to crushing and pinching, while still allowing the conduit tobe light and flexible. A cross section of the wall of an example of sucha conduit is shown in FIG. 1.

It is advantageous to manufacture this type of conduit as a continuousprocess. In the prior art this is achieved by the spiral winding of athin polymer tape (ribbon or film) onto a former such that the edges ofadjacent layers overlap a small amount. A bead of molten polymer is thenapplied over top the overlapping edges welding them together andsimultaneously forming the helical reinforcing ribs. A disadvantage withthis forming technique is the difficulty welding several adjacentlayers. This problem is especially severe when multiple layer conduitwalls are to be formed. While combining the application of a molten beadwith another secondary thermal welding process or applying the polymerto the former as a still molten plastic does go some way to alleviatingthis difficulty, these solutions add complexity to the tube former andmay be difficult to achieve with very thin walls.

SUMMARY OF THE INVENTION

The present invention provides a conduit, with particular application tothe limbs of a breathing circuit, which will at least go some waytowards improving on the above or which will at least provide the publicand the medical profession with a useful choice, and/or to provide amethod of manufacturing conduit which will at least go some way towardsproviding the public and manufacturers with a useful choice.

In a first aspect the invention may broadly be said to consist in amethod of continuously forming conduit comprising:

continuously applying at least one thin film ribbon, each having“leading” and “trailing” lateral edges, spirally around a formerrotating and advancing said conduit, with the leading edge of each turnof ribbon overlapping the trailing edge of a previous turn of ribbon onthe former and the trailing edge of each turn under lapping the leadingedge of a succeeding turn, while,

in advance of said overlapping of said turns, applying a bead of moltenplastic, having “leading” and “trailing” edges, adjacent the exposedtrailing edge of the most recently applied turn on said former, suchthat said bead is interposed between the overlapping and under lappingportions, said bead when cooled forming a helical reinforcing bead, andwherein

said overlapping portion is supple, at least laterally, and conformsaround the contour of said molten bead as it is applied thereto, suchthat said overlapping portion continuously contacts said bead and bondsalong said conforming portion; and said overlapping portion of saidribbon meets or substantially meets said trailing edge of said underlapping portion of said ribbon, at the trailing edge of said bead.

Preferably said leading edge of said over lapping ribbon meets orsubstantially meets said under lapping ribbon at the leading edge ofsaid bead.

Preferably said conduit is reinforced against crushing, and saidreinforcement consists of said polymer bead.

Preferably said ribbon is a breathable plastic material.

Preferably said ribbon is a laminate where a layer of breathable plasticmaterial is laminated to a reinforcing layer which also allows thepassage of water vapour.

Preferably said thin film ribbon has a thickness of less than 50microns.

Preferably said method further comprises the steps of,

applying one or more heating wires to the exposed trailing edge of theribbon prior to applying the bead, such that the bead encapsulates thesaid one or more heating wires onto the said trailing edge.

Preferably the former includes a plurality of rotating rods spaced aboutan axis and acting to support and advance the conduit during forming,further comprising:

first applying a sacrificial layer of thin plastic directly around saidformer, before said conduit is formed on said former over top of saidsacrificial layer, and

subsequent to forming said conduit, removing said sacrificial layer frominside said thin walled conduit after cooling.

Preferably said sacrificial layer is a thin ribbon having “leading” and“trailing” lateral edges, and said sacrificial layer is spirally woundaround said former in a continuous fashion, with the leading edge ofeach turn of said sacrificial layer overlapping the trailing edge of aprevious turn of said sacrificial layer on the former and the trailingedge of each turn under lapping the leading edge of a succeeding turn.

Preferably said sacrificial layer is of a material having a differentbase polymer than that of said conduit, such that no substantialadhesion occurs when adjacent layers of said sacrificial layer and saidconduit are heated.

To those skilled in the art to which the invention relates, many changesin construction and widely differing embodiments and applications of theinvention will suggest themselves without departing from the scope ofthe invention as defined in the appended claims. The disclosures and thedescriptions herein are purely illustrative and are not intended to bein any sense limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional side elevation of a wall of a conduitaccording to an embodiment of the prior art.

FIG. 2 is a cross sectional elevation of a wall of a conduit accordingto one embodiment of the present invention.

FIG. 3 is a plan view of a conduit forming device for forming areinforced conduit according to a further embodiment of the presentinvention, such as the conduit pictured in FIG. 2.

FIG. 4 is a cross sectional elevation of a conduit wall showing a roughinner surface resulting from the tape not completely following thecontour of the molten bead.

FIG. 5 is a side elevation of a conduit according to a furtherembodiment of the present invention including outer axial reinforcingthreads.

FIG. 6 is a plan view of a conduit forming device for forming areinforced conduit according to an embodiment of the present invention,such as the conduit pictured in FIG. 5.

FIG. 7 is a cross sectional side elevation of a conduit wall accordingto a further embodiment of the present invention including a pair ofheater wires within the conduit wall.

FIG. 8 is a plan view of a conduit forming device for forming theconduit pictured in FIG. 7.

FIG. 9a is a cross section of a tape or ribbon illustrating the assemblyof a pre-formed tape including a pair of heater wires according to afurther embodiment of the present invention.

FIG. 9b is a cross section view of the pre-formed ribbon of FIG. 9a ,shown assembled.

FIG. 10 is a cross section view of a conduit wall including a pair ofheater wires formed from the pre-formed ribbon shown in FIG. 9 b.

FIG. 11 is a cross sectional elevation of a conduit wall showing adefect caused by the bead flowing between overlapping adjacent layers.

FIG. 12 is a plan view of an apparatus for removing the sacrificiallayer.

FIG. 13 is a plan view of the apparatus of FIG. 12, shown with a conduitovertop.

DETAILED DESCRIPTION

The present invention relates to breathing conduits in general and inparticular to improved methods of forming thin film (tape or ribbon)spiral wound conduits. Consequently the present invention findsapplication in breathing conduits fabricated from a variety of materialswhich may include breathable and/or non-breathable materials (breathablematerials being capable of transmitting water vapour but not liquidwater).

In assisted breathing, particularly in medical applications, gaseshaving high levels of relative humidity are supplied and returnedthrough conduits of a relatively restricted size. Build up ofcondensation on the inside wall of the conduit is a potential result ofthis high humidity. The purpose of including a breathable region orregions in the conduit wall is to allow diffusion of water vapour fromthe expiratory limb of the breathing circuit along the path thereof.This can reduce the build up of condensation within the expiratory limbby drying the humidified gases during their flow through the expiratorylimb. This furthermore reduces the humidity of the gases arriving atancillary equipment, such as filters, ventilators and the like, reducingthe risk of condensation accumulation, thereby improving theiroperation, or alleviating potential detrimental effects.

The preferred breathable material is a hydrophilic polyester formed intoa homogeneous flat film or ribbon. This material has been foundparticularly suited to thin film productions having a wall thickness ofless than approximately 50 microns, and therefore find particularsuitability in the manufacturing methods of the present invention. Itwill be appreciated that other breathable materials may also be suitablefor forming breathable conduits. Such breathable materials may bebreathable due to their composition, physical structure or a combinationthereof.

The following embodiments will be described with particular reference tobreathable thin film wall construction from materials such as thosereferred to above. It will be appreciated however, that in the followingdescribed embodiments the material used to form the conduit walls may beeither breathable or non-breathable and may also include combinations ofboth breathable and non-breathable materials. It will be alsoappreciated for the following described embodiments that the film(s)supplied to the former may be supplied either as a preformed flat ribbonwound onto a reel or may alternatively be supplied directly to theformer from an extruder. Each of these options may have associatedadvantages and disadvantages which will be discussed later. It will alsobe appreciated by those skilled in the art that the materials suppliedto the former may require a number of guides tensioners and/or rollersin order to position the materials accurately and provide the necessarytension.

As a corollary of material cost it is preferred that the conduit wall bemanufactured to have a relatively low wall thickness, so much so thatthe conduit wall membrane may be insufficiently sturdy to be selfsupporting. Spiral or helical reinforcing members are therefore providedas part of the tubular membrane to provide support. The helical orspiral supporting members (beads) are formed from polymer materials andmay be of the same material used in the wall of the conduit or any othercompatible plastics material.

Referring to FIG. 1, the lay-up arrangement of a flexible breathingconduit known in the art is shown. Referring to FIG. 2, a breathingcircuit limb wall cross section is shown with a thin film flexible wall.The thin film or ribbon is arranged in a spiral or helix such that theedge portions 45, 46 of adjacent layers overlap and form the wall of atube. Interposed the overlapping edges 45, 46 of adjacent winds ofribbon, is a bead of polymer material bonded with the overlappingportions of ribbon sealing the joint between windings and forming acontinuous tube. The seam is formed between the edge of a first layer offilm and the edge of a second, adjacent layer of film which is laid overtop of the polymer bead while the bead is molten. The overlapping layerof film because it is so thin, closely follows the contour of the beadand results in a smooth inner conduit wall. It is desirable for theribbon to be sufficiently supple at least laterally, to conform alongits overlapping portion to the contour of the head, so that theoverlapping ribbon may meet or substantially meet the under lappingribbon at the edge of the bead.

The accompanying figures show small gaps or spaces between thereinforcing bead and the overlapping portion of ribbon. It is to beunderstood that these spaces are present for illustration purposes only,in order to differentiate the bead from the overlapping layer in thediagrams. In practice the overlapping layer conforms to the bead andbonds, without forming large gaps or bubbles.

An example of continuous forming apparatus suitable for manufacturingthe breathing tube according to a first embodiment of the presentinvention described in FIG. 2 is shown in FIG. 3. The apparatus includesa former 1 preferably of a known type including a plurality of rotatingrods arranged around a central support rod. The rods extend from and arerotated by a gearbox within a machine stock 2. At least in the tubeforming region the rotating rods follow a helical path. The pitch angleof the rods relative to the support rod controls the pitch angle of thetube being formed. An example of such a machine is a spiral pipelinemandrel available from OLMAS SRL of Italy.

Tube being formed on the former is rotated and advanced in the directionof arrow 3 by the movement of the rotating rods. The advance speed ofthe former is selected relative to the rotational speed so that thepitch of the helical laying of the strip or tape on to the former 1 is alittle less than the width of the strip so that adjacent turns narrowlyoverlap. A first extruder 4 supplies a tape or ribbon 5 of thin filmpolymer materials with a preferred width of approximately 10millimetres. It will be readily understood that variation from thispreferred ribbon width and size of overlap is possible in order toachieve reinforcing beads or conduits having varying pitches and/ordimensions. The ribbon 5 deposits on the former 1 in a helical fashionby action of the former. The pitch of the helical disposition of ribbon5 is slightly less than the width of ribbon 5 and results in preferredoverlap of approximately 2.5 millimetres. The helical deposition ofribbon 5 forms the wall 6 of the conduit.

An extruder 7 extrudes a bead 8 of molten or semi-molten polymermaterial. The molten head 8 deposits between the overlapping portions ofadjacent winds of ribbon 5 and is sufficiently heated to weld the stripsof ribbon 5. In the preferred embodiment of the present invention thedimensions of the molten bead 8 are approximately 2.5 millimetres wideand 1.5 millimetres high. The conduit formed according to a preferredembodiment has an approximate internal diameter of 19 millimetres,although it will be appreciated that the methods of the presentinvention may be suitable for forming conduits having thin walls,irrespective of diameter of the conduit or the dimensions of thereinforcing bead.

For breathable wall conduits the thickness of the breathable film orribbon 5 must be thick enough so that the conduit does not become tooflimsy in use, but must also be thin enough so that the conduit wall issufficiently breathable. It has been found that with polyester blockcopolymers, such as those described above, a wall thickness between 15and 35 microns fulfil these requirements. The preferred wall thicknessfor breathable conduits according to the present invention isapproximately 25 microns. A wall thickness of 25 microns has been foundto provide a useful balance between breathability, flexibility andstrength. The wall thickness for providing an optimal compromise ofproperties will ultimately depend on the specific material employed. Inthis regard the materials and preferred dimensions referred to in thedescription are illustrative and are not intended to be in any waylimiting.

During the continuous manufacture of breathing conduits according to themethod described above it has been found that overheating problems mayoccur when thin film (whether breathable or not) is used in the conduitwalls. Further, the action of the helical rods rotating and advancingthe conduit, may wrinkle or even damage the thin ribbon deposited on theformer and may reduce the finish quality of the conduit. The mandreltemperature is raised by the continuing application of the molten beadwhich may also result in the thin film overheating and sticking to themandrel or rotating rods, causing the quality of the conduit wall tosuffer and/or disrupting the forming process. In order to overcome thesepotential problems it has been found that a sacrificial layer, woundonto the mandrel in an overlapping helix pattern before the applicationof the film reduces these problems and increases the quality of theconduit produced.

In order to accomplish this task the sacrificial layer of tape issignificantly more rigid compared to the conduit wall and must notpermanently stick to the mandrel or to the inside of the conduit wall.It has been found that a material such as bi-axially orientatedpolypropylene is ideally suited for the sacrificial layer. It will beappreciated that many alternative materials having a different basepolymer to that of the conduit wall may also be suitable. The preferredthickness of the polypropylene sacrificial layer is betweenapproximately 20 and 60 microns.

Referring to FIG. 3, a sacrificial layer 17 is wound from reel 16 ontothe former before the breathable extruded tape 5. The heat from theapplied molten bead may weld the overlapping layers of sacrificial layerto each other, but does not result in any significant bonding betweenthe sacrificial layer and the conduit wall. Alternatively, a secondarythermal welding process may be employed to weld the overlapping layersof sacrificial tape before the conduit is formed overtop. Thesacrificial layer may perform many additional advantageous functionssuch as those described below:

-   -   1. The dummy layer protects the helically arranged rotating rods        on the mandrel from being fouled by molten plastic.    -   2. The sacrificial layer increases the stability of the process        and may help prevent the overlapping layers that form the        conduit wall from slipping and moving relative to each other.    -   3. The sacrificial layer provides a protective harrier between        sharp edges or small protrusions on the mandrel or rotating        rods, and the film or ribbon.    -   4. The sacrificial layer shields the thin film from the higher        operating temperatures of the mandrel and reduces overheating of        the film.

It will be readily appreciated by those skilled in the art that thebenefits derived from the application of a sacrificial layer onto themandrel before forming a conduit, are not limited only to materiallay-up and construction wherein the helical reinforcing bead isinterposed the overlapping layers.

The polypropylene layer can be easily removed from the inner wall of thefinished conduit product after cooling as it does not bond significantlyto the conduit. Additional means such as water cooling of the mandrelmay also be provided to reduce overheating.

A method of removing a releasable inner layer (for example thesacrificial layer 17) from within a length of conduit 37, subsequent toforming the conduit, will be described with reference to FIGS. 12 and13. A shaft 39 is provided having a substantially hollow cylindricalshape of a length longer than that of the desired conduit productlength. The shaft 39 has a longitudinal slot 40 and is cantilevered fromstock 42. The slot of shaft 39 is in fluid connection with a suction orvacuum source 38 via stock 42.

The outer diameter of the shaft is preferably smaller than that of theconduit 37. A tapered shoulder region 41 is provided at the built-in endof the shaft 39 in order to enable an effective seal to be formedbetween the inner layer and the shoulder portion when suction isapplied. Alternatively, the seal may be formed between the shaft and theoutside of the conduit. The effect is to seal (so far as necessary) atleast the inside of the releasable inner layer from the surroundings.

In use, and in order to remove the sacrificial layer 17 from the innerwall of the conduit 37, without damaging the conduit wall, the conduit(including sacrificial layer) is placed overtop the shaft as shown inFIG. 13. An end of the conduit is slid over the shoulder portion 41 ofthe shaft 39 forming an adequate seal. The other end of the conduit ispulled back in an axial direction so that the conduit is contracted asshown in region 42, exposing and separating the end portion ofsacrificial layer 17 from the conduit. Vacuum source 38 applied to theinner space of the shaft, leads to a pressure differential between theinside and the outside of the inner layer where it has separated fromthe conduit. This urges the inner layer onto the shaft, and into theslot, and the separation propagates along the length of the section ofconduit, sucking the sacrificial layer from the inner wall of theconduit 37. The portion of sacrificial layer 17 immediately oppositeslot 40 is sucked so that it protrudes into the shaft interior. It maybe necessary to initiate this release process at the exposed end (freeend of the shaft) of the sacrificial layer 17 by hand (by bringing theseparated end portion of the inner layer adjacent the slot. Helicalreinforcing bead 43 prevents the conduit itself from being drawn intoslot 40). After release of the sacrificial layer from the inner wall ofthe conduit 37, the conduit can be easily removed by sliding it off theshaft. Removal of the vacuum from the shaft allows removal of theremaining sacrificial layer more easily.

Applying the molten bead between the overlapping layers of tape insteadof over the top of the overlapping layers may improve the weld quality,as both layers of tape that are to be welded are in physical contactwith the molten bead. This lay-up may also reduce overheating problemsby lowering the temperature necessary to properly bond the molten head.When the prior art forming method shown in FIG. 1 is employed tomanufacture conduits from very thin film or ribbon, (for example, havinga wall thickness less than approximately 50 microns), consistentlyproducing a high quality surface within the conduit has been found to beproblematic.

FIG. 4 and FIG. 11 illustrates some potential problems which may occurduring the production of conduit resulting in inferior wall smoothness.The quality of the surface finish for the inner surface of a breathingconduit is important, because rough inner surfaces may hinder gases flowand may cause more condensation to build up in the conduit. A protrudingor flapping portion 33 may result if the underlapping layer of film isnot completely bonded to the molten bead. This problem may occur if theunderlapping portion of film is too wide or positioned on the formerincorrectly. Similarly, overflow of molten bead 35, may result in aprotrusion or defect 34, if the underlapping portion 36 of the underlapping layer does not extend far enough under the head. Small voids 9or undulations, may result between adjacent strips of ribbon if the filmdoes not closely conform to the contour of the molten head. This mayoccur if the thin ribbon is not sufficiently supple. For this reason theconstruction technique of the present invention is especially suited toconduits fabricated from thin supple film. The thin film is highlyflexible and able to conform closely to the shape of the raised rib ofthe applied molten bead 8 during fabrication. By lapping very closely onto the bead and wrapping around the bead, the thin film maintains asmooth inner surface on the finished conduit product. A further defect44, is shown where the overlapping portion of the layer overlaps thebead too much. The molten head will also flow to fill voids orundulations between the lay-up, resulting in a smooth conduit wall. Itwill be appreciated that the conduit wall cross section shown in FIG. 2and FIG. 11 is illustrative and not meant to be interpreted strictly inregard to the space shown between the bead and the conduit wall layers.The application of a sacrificial layer onto the former before theconduit wall is formed, is especially suited to the conduit formingmethod wherein the molten head is applied between overlapping layers.The presence of the sacrificial layer ensures that the helicallyarranged rotating rods on the former do not become fouled with moltenpolymer.

Throughout the diagrams, the helical reinforcing bead is shown as havinga substantially semi-circular cross section. It is however envisagedthat the actual cross sectional shape of the reinforcing head may vary.For example the presence and thickness of the film which overlaps thereinforcing head, may affect the shape of the reinforcing bead byflattening the bead, resulting in a less rounded and more square orrectangular cross section. Further, rollers may be employed to shape thebead. The semi-circular reinforcing bead shown in the accompanyingdrawings is purely illustrative and not intended to be in any waylimiting.

It has been found that breathing conduits formed according to the firstpreferred embodiment described above are extremely light, flexible andprovide good crush resistance. However conduits having very thin wallsmay have a reduced resistance to axial deformation and/or stretching.Due to the thin tape used to form the walls of the conduit, theresulting product may be prone to expansion and/or contraction along theaxis of the conduit. In use axial forces arising from patient breathingare capable of producing axial extension/contraction along the length ofthe conduit. In order to improve the axial stiffness of such breathingconduits, a further embodiment will now be described.

In a further embodiment shown in FIG. 5 a plurality of reinforcingthreads 10, running the length of the wall and spaced around theperimeter of the tube are aligned parallel to one another andsubstantially parallel to the major axis of the conduit. The threads 10are supported by the helical bead 11, with the threads spanning thespaces between turns of the helical head. In this embodiment it is maybe desirable to choose the reinforcing threads (material, gauge, typeand number) such that the threads are sufficiently stiff to improve theconduits ability to resist buckling under the transiently reducedinternal pressures that could be expected during patient breathing.Unrestrained or excessive buckling of the threads may result inunacceptable levels of conduit axial contraction and/or extension. Theaxial threads 10 may be spun or braided fibres or drawn or extruded monofilaments or other equivalent forms. Tensile reinforcement may beprovided by braided or spun fibres while compressive and/or flexuralreinforcement may be provided by drawn or extruded mono filaments.

A method of forming the tube according to the embodiment of FIG. 5 isdescribed with reference to the apparatus shown in FIG. 6. In particularin the machine of FIG. 6 the tube 12 is formed by helically wrapping apreformed tape or strip of polymer 13 on to a rotating former 14. Thestrip 13 unrolls from reel 15. In an analogous manner to that describedpreviously for the first preferred embodiment, a sacrificial layer ofpolypropylene 17, is wound in an overlapping helix onto former 14 fromspool 16. The sacrificial layer 17, between the mandrel and the conduitbeing formed, allows the extremely thin film to be shielded from themandrel and higher operating temperatures.

Tube being formed on the former is rotated and advanced in the directionof arrow 3. The advance speed of the former is selected relative to therotational speed so that the pitch of the helical laying of the strip ortape on to the former 14, is a little less than the width of the stripso that adjacent turns narrowly overlap. An extruder 18 extrudes a bead19 of molten polymer material. The molten bead 19 deposits between theoverlapping portions of adjacent winds of tape 13 and is sufficientlymolten to weld to the strips of tape 13. The molten bead becomes thehelical reinforcement for the finished conduit.

A freely rotatable thread laying head 20 is located over the formerafter the bead extruder 18. The rotating head 20 carries a plurality ofspools 21 holding reinforcing thread. The head 20 is rotatable by anelectric motor and drive belt 22 and 23 respectively. The head 20 ispreferably rotated at a speed synchronized with the speed of effectiverotation of the product 12. Advancement of tube along the former 14draws thread 24 from the spools 21 to be laid as parallel threads 10 onthe outside of the reinforcing head 19. Another thread 25 is drawn fromspool 26 and wound onto the former overtop of the longitudinal threads10, laid by thread laying head 20. The thread 25 is laid on the formerin a helical pattern such that the thread lies between the helical beadof molten polymer extruded from extruder 18. The purpose of thread 25 isto provide a temporary means of securing the plurality of longitudinalthreads in position in preparation for permanent fixing. A secondextruder 27 extrudes a second bead of molten polymer material 28 anddeposits it over top the plurality of reinforcing threads 10 anddirectly on top of the first reinforcing bead 19 and bonds. The secondbead of molten polymer sandwiches the plurality of longitudinal threadsbetween itself and the first reinforcing rib formed by polymer bead 19.Thread 25 however, lies between these overlapping reinforcing beads anddoes not become permanently bonded to the conduit wall, allowing it tobe removed. Thread 25, may be discarded or drawn from the former in aposition subsequent to the application of the second reinforcing bead 28and wound onto a spool for re-use.

This embodiment of the invention provides a breathing circuit limbreinforced against crushing by the helical bead and against longitudinalextension by the axial threads 10 as well as providing a breathingconduit having all the advantages of the first preferred embodiment. Thespanning threads 10 also provide an additional advantage by reducingdirect contact between the user/environment and the surface of the tube,therefore reducing the risk of punctures and damage. The threadseffectively provide an additional barrier against potential damagearound the conduit wall. It will be appreciated that the foregoingmethod of reinforcing a conduit is not limited to conduits wherein thehelical reinforcing bead is interposed between the overlapping layers.

A further breathing circuit component to which the present invention maybe applied is catheter mounts. A catheter mount connects between apatient interfacing component such as a mouth piece, nasal mask orendotracheal tube and the dual limbs of the breathing circuit.Connection with the dual limbs of the breathing circuit is generally viaa wye connector. The extreme flexibility of very thin walled tubesmanufactured according to the methods herein, makes them particularlyuseful in a catheter mount component.

It should be appreciated that with all of the forming methods describedinvolving winding of a narrow ribbon or strip to create a tube, it wouldbe possible to wind two or more ribbons or films simultaneously onto theformer so that the turns created by each ribbon are interposed by turnsof other ribbons, edges overlapping and being bonded together by aninterposed extruded helical rib. For example a pair of ribbons may belaid as a double helix. This would require a multiplication in thenumber of forming stations associated with the wound on components ofthe tube or conduit. Further it is envisaged that for methods where apreformed tape is supplied to a former, the tape may be provided as alaminate having a thin film layer and a reinforcing layer bonded to it.Where the thin film layer is a breathable layer, the reinforcing layeris also permeable and allows the passage of water vapour.

A further embodiment of the present invention is envisaged where thinwalled breathing conduits are manufactured in a similar manner asdescribed above hut, where the conduit wall also preferably contains atleast one thin conductive wire. A pair of wires may be included in orderto provide a means for heating the conduit and or to carry electricalsignals to sensors or transducers. Heated conduits may reduce the buildup of condensation in the conduit and may also offer a means tomaintaining the temperature of humidified gases flowing through theconduit. Heated conduits are most often used in only the inspiratory armof a breathing circuit but can also be used in the expiratory arm.Heated wall conduits may also be components of coaxial (unilimb)circuits, or be used in single limb applications such as for CPAPtherapy. In such breathing conduits where the inspiratory arm includesheater wires, the corresponding connectors at at least one end of theconduit will include an electrical connection suitable for connectionwith the humidified gases source in order to supply electrical energy tothe conduit heater wires. Referring to FIG. 7, a breathing conduit isshown including a pair of heater wires 31, embedded in the helicalreinforcing bead.

A method of forming a conduit according to this embodiment of thepresent invention including a pair of heater wires will now be describedwith reference to FIG. 8. The method is similar to the method previouslydescribed and illustrated in FIG. 3, but an additional stage is requiredto lay a pair of parallel wires in between the overlapping adjacentwinds of film in the edge area of the film that will become the seam. Apair of wires 31 are supplied from two reels 29 and 30. The wires arelaid on top of the first wind of film, towards the edge, after it islaid on the former but before the molten bead is applied. FIG. 8 shows apair of heater wires 31 in hidden detail under the molten bead 8. Themolten bead 8 is then laid over the wires on top of the first layer offilm before the following overlapping wind of film wraps around theformer and completes the tube. It will be appreciated that each of thefilm, heating wire(s), and reinforcing bead may be applied in adifferent plane in order to achieve the desired spatial lay-up.

The resulting conduit is shown in FIG. 7 and is similar to the previousembodiment shown in FIG. 2, but includes an additional pair of heaterwires embedded in the helical reinforcing bead of the conduit wall. Inthis embodiment, a sacrificial layer 17 may also be wound in anoverlapping helix onto the former from spool 16. The sacrificial layer17 may be a polypropylene layer or some other material that will notweld to the conduit wall. The sacrificial layer 17 between the mandreland the conduit being formed, allows the extremely thin film to beshielded from the higher operating temperature of the mandrel andalleviates overheating of the film.

A further method of forming a conduit according to the present inventionincluding a pair of heater wires will now be described.

The above method of forming a conduit discloses an online process forwinding a pair of heater wires into the conduit wall. It is envisagedthat a pair of heater wires may be included in a preformed tape whichwould then be used to form the walls of the conduit in a similar methodto that described above and illustrated in FIG. 3. FIGS. 9a and 9b showcross sections of such a tape being formed by laying a pair of parallelwires a distance x from one edge of the tape. The length x of tapebetween the wires and the edge is then folded over and back onto therest of the tape so as to enclose the pair of parallel wires, as shownby arrow 32. A secondary thermal welding process may then be employed tobond the folded portion of tape so as to permanently embed the parallelwires. It will be appreciated however that a secondary thermal weldingprocess may not be necessary if the extruded tape is molten orsemi-molten when the folding occurs. In this case the two regions ofmolten layer, when folded and pressed together will bond.

Such a pre-formed folded tape including embedded wires may then be woundon to reels and supplied to a conduit forming process such as thatdescribed previously and illustrated in FIG. 3 to produce a breathingconduit with a pair of integral heating wires. FIG. 10 shows the lay-upof a breathing conduit formed by this embodiment of the presentinvention. The portion of thin film that wraps over the reinforcing beadand the adjacent wind on the former is only one layer thick andtherefore is able to conform to the contour of the reinforcing bead. Atube formed according to this embodiment of the present inventiontherefore is able to retain all of the advantages of the previouslydescribed preferred embodiments, while having the additional advantagethat a forming apparatus as described in FIG. 3 may be employed tomanufacture a conduit including embedded heater wires withoutsubstantial modification to the forming apparatus. In such a case theextruder 4 is replaced with a reel of pre-formed folded tape such asthat shown in FIG. 9b and supplied to the forming apparatus.

The invention claimed is:
 1. An apparatus for continuously formingconduit, the apparatus comprising: a former configured to receive atleast one ribbon, and to draw the ribbon around and advance the ribbonalong to form a helical arrangement of the ribbon, a pitch of thehelical arrangement being less than width of the ribbon, a firstassembly configured to deliver a first ribbon comprising a plasticmaterial to the former at a first position on the former, a secondassembly configured to deliver continuously a molten bead to the formerat a second position less than one turn pitch from the first position ofdelivery of the first ribbon, the second position corresponding to anexpected position of a trailing edge of the first ribbon delivered bythe first assembly, and a reel configured to deliver a sacrificial layerto the former in an overlapping pattern at a third position, wherein thethird position is located in front of the first position so that thesacrificial layer is delivered to the former before the first ribbon isdelivered to the former.
 2. The apparatus for continuously formingconduit of claim 1, wherein the first ribbon comprises a leading lateraledge and a trailing lateral edge, and the former is configured toarrange the first ribbon in spiral turns such that, at a first spiralturn, the leading lateral edge overlaps the trailing lateral edgeadjacent a previous spiral turn, and the trailing lateral edge underlapsthe leading lateral edge adjacent a succeeding spiral turn.
 3. Theapparatus for continuously forming conduit of claim 2, an extent of theleading lateral edge over the trailing lateral edge defining anoverlapping portion and an extent of the trailing lateral edge under theleading lateral edge defining an underlapping portion, wherein thesecond assembly is configured to interpose helically the molten beadbetween the overlapping portion of the first ribbon and the underlappingportion of the first ribbon.
 4. The apparatus for continuously formingconduit of claim 3, the molten bead comprising a first edge and a secondedge, wherein the second assembly is configured to deliver the moltenbead such that the molten bead, when cooled, comprises: a first portion,comprising a flat portion having a flat profile in cross-section,proximal the underlapping portion of the first ribbon and comprising afirst edge and a second edge, and a second portion, having a contourprofile in cross-section, proximal the overlapping portion of the firstribbon and extending between the first edge and the second edge of thefirst portion of the cooled bead.
 5. The apparatus for continuouslyforming conduit of claim 4, wherein the leading lateral edge of thefirst ribbon meets the underlapping portion of the first ribbon at thefirst edge of the first portion of the cooled bead.
 6. The apparatus forcontinuously forming conduit of claim 4, wherein the leading lateraledge of the first ribbon meets the underlapping portion of the firstribbon at the first edge of the first portion of the cooled bead.
 7. Theapparatus for continuously forming conduit of claim 1, wherein the firstassembly comprises an extruder.
 8. The apparatus for continuouslyforming conduit of claim 1, wherein the molten bead comprises a plasticmaterial.
 9. The apparatus for continuously forming conduit of claim 1,wherein the plastic material of the first ribbon is breathable, suchthat, when the conduit is in use, the plastic material of the firstribbon allows passage of water vapor from a respiratory gas flowingwithin the conduit.
 10. The apparatus for continuously forming conduitof claim 1, wherein the second assembly comprises an extruder.
 11. Theapparatus for continuously forming conduit of claim 1, wherein the firstribbon has a thickness of less than about 50 microns.
 12. The apparatusfor continuously forming conduit of claim 1, further comprising a thirdassembly configured to deliver a pair of spaced apart heater wires inbetween adjacent turns of the helical arrangement of the ribbon and in aposition that will be overlaid by the molten bead from the secondassembly.
 13. An apparatus for continuously forming conduit, comprising:a former configured to receive a ribbon, the former configured to drawthe ribbon around and advance the ribbon along, to form an overlappinghelical arrangement of the ribbon, pitch of the helical arrangementbeing less than width of the ribbon, a first assembly configured todeliver a first ribbon to the former, at a first location, a secondassembly configured to deliver a second ribbon to the former, at alocation after the first ribbon, a bead assembly configured tocontinuously deliver a molten reinforcement bead to the former at aposition less than one turn pitch from a position of delivery of thesecond ribbon, the position corresponding to an expected position of atrailing edge of the second ribbon, wherein the molten reinforcementbead is configured to provide reinforcement to the conduit, and a reelconfigured to deliver a sacrificial layer to the former in anoverlapping pattern at a third position, wherein the third position islocated in front of the first position so that the sacrificial layer isdelivered to the former before the first ribbon is delivered to theformer; wherein the first ribbon and the second ribbon each have athickness of less than about 50 microns.
 14. The apparatus forcontinuously forming conduit of claim 13, wherein the apparatus isconfigured such that no material is applied outside of the first ribbonbefore the first ribbon is overlaid by the second ribbon.
 15. Theapparatus for continuously forming conduit of claim 13, wherein thesecond ribbon comprises a leading lateral edge and a trailing lateraledge, and the former is configured to arrange the second ribbon inspiral turns such that, at a first spiral turn, the leading lateral edgeoverlaps the trailing lateral edge adjacent a previous spiral turn, andthe trailing lateral edge underlaps the leading lateral edge adjacent asucceeding spiral turn.
 16. The apparatus for continuously formingconduit of claim 15, an extent of the leading lateral edge over thetrailing lateral edge defining an overlapping portion and an extent ofthe trailing lateral edge under the leading lateral edge defining anunderlapping portion, and the molten reinforcement bead comprising afirst edge and a second edge, wherein the bead assembly is configured todeliver the molten reinforcement bead such that the molten reinforcementbead, when cooled, comprises a first portion, comprising a flat portionhaving a flat profile in cross-section, proximal the underlappingportion of the second ribbon and comprising a first edge and a secondedge, and a second portion, having a contour profile in cross-section,proximal the overlapping portion of the second ribbon and extendingcontinuously between the first edge and the second edge of the firstportion of the cooled reinforcement bead.
 17. The apparatus forcontinuously forming conduit of claim 16, wherein the extent of theoverlapping portion of the second ribbon conforming around the fullperimeter of the second portion of the helical reinforcement beaddefines a conforming portion that is bonded to the cooled reinforcementbead along the conforming portion.
 18. The apparatus for continuouslyforming conduit of claim 13, wherein the second ribbon comprises abreathable plastic material that, when the conduit is in use, allowspassage of water vapor from a respiratory gas flowing within theconduit.
 19. The apparatus for continuously forming conduit of claim 13,wherein the first assembly comprises a reel.
 20. The apparatus forcontinuously forming conduit of claim 13, wherein the second assemblycomprises an extruder.
 21. The apparatus for continuously formingconduit of claim 13, wherein the bead assembly comprises an extruder.22. The apparatus for continuously forming conduit of claim 4, whereinthe second assembly is configured to deliver continuously the moltenbead such that the overlapping portion of the first ribbon conformsaround and continuously contacts the full perimeter of the secondportion of the cooled bead and meets the underlapping portion of thefirst ribbon at the second edge of the first portion of the cooled bead.23. The apparatus for continuously forming conduit of claim 13, whereinthe molten reinforcement bead is configured to reinforce the conduitagainst crushing when the molten reinforcement bead is cooled.